The latest death has baffled investigators and forced experts to rethink their assumptions

The theory about how the country's anthrax attack unfolded last month seemed pretty plausible. Yes, the story had loose ends, but the basic idea was that anyone who'd come down with the disease had either been in direct contact with letters laced with spores or had been in a room that a letter passed through.

That was before Kathy Nguyen died. On Thursday, Oct. 25, the Vietnamese-born hospital worker came down with chills and muscle aches. She went to work Thursday and Friday at the stockroom of the Manhattan Eye, Ear & Throat Hospital on Manhattan's Upper East Side. But the...